Stamping Press

ABSTRACT

A stamping press includes a fixed lower body with a machine bed, a mobile upper body or press carriage, a lower cushion which constitutes a mobile body in respect of the lower fixed body, an upper cushion which constitutes a mobile body in respect of the upper mobile body, a die-cutting assembly formed of the top part of the die-cutting assembly integral to the upper mobile body, and a bottom part of the die-cutting assembly integral to the machine bed, and a guiding device ( )for the top part of the die-cutting assembly in respect of the bottom part of the die-cutting assembly, the lower cushion including a single hydraulic cylinder with an annular section fitted in the central part of the machine bed, hollow in the centre, this central part constituting the zone for removal of scrap or cuttings produced by the die-cutting performed in the stamping process.

This invention refers to a high precision press for stamping sheet metalfitted with a set of items representing major advantages in respect ofthe state of the art, including a single central hollow lower ram whichprevents unbalances in the stamping operation, and enables theevacuation of scrap, upper and lower adapter plates, a lower bottomingdie on the bed plate or bolster, upper and lower punch holder plates andan attached die on a die shoe plate.

The devices currently available on the market are used for manufacturingprecision items which comply with most of the requirements made by thefinal user, but are nevertheless not free from certain technicalproblems during the manufacturing process.

STATE OF THE ART

U.S. Pat. No. 4,267,753 discloses a set of apparatus for producing astamped item from a strip, which comprises a lower stripper, driven by aset of spiral springs and a central spring for operating the upperstripper. This type of cutting is commercially known as GRIP FLOW®.

U.S. Pat. No. 4,905,556 discloses a stamping press comprising upper andlower central hydraulic cylinders for operating the strippers, with theexpulsion of the workpieces and the scrap or cuttings taking placetogether from the lower machine bed upwards. This also comprises atightening ring for securing the material around the workpiece duringthe stamping operation. This cutting system is known as “fineblanking”.

WO 01/00396 describes a device for cutting pieces from a sheet ofmaterial, which comprises a press and is provided with a set ofhydraulic cylinders and at least one additional cylinder forcompensation at the bottom.

U.S. Pat. No. 6,370,931 describes a press practically identical to theone of U.S. Pat. No. 4,267,753, but in which the spiral springs havebeen replaced by hydraulic cylinders.

In accordance with the “fineblanking” system, the so-called scrap orcuttings are expelled along with the finished part. For this reasonthere later has to be a second “pumping” or similar operation through asieve to separate the scrap or cuttings from the finished pieces. Thisleads to a great risk of “banging” the finished parts in the sievingprocess that may cause deterioration of the manufactured part. Thiscircumstance requires strict quality control. Furthermore, when a pieceof scrap gets stuck in the stamping zone this could damage the die, oreven the press. According to this manufacturing method the material formaking the part is manipulated in such a way that the most importantwaste from the strip known as “scrap” is expelled in a single direction,while the workpieces and cuttings are expelled together. There are thusonly two channels for expulsion for the waste and finished parts, withfinished parts and cuts mingling, at the risk of sending finished partsto the customer along with cuttings, especially in automobile parts.

The manufacturing processes known as “fineblanking” tend to use atightening ring known as “V-ring”. The purpose of this tightening ringis to stick a V-shaped wedge into the material surrounding what will bethe finished part in such a way that this locks the material prior tobeing “punched”. This minimises the deformations in the materialsurrounding the final part and thus minimises the deformations in thefinished part itself. This is not however the case according to theinvention, as will be described below. This manufacturing system entailsgreater consumption of raw material that can in some cases reach a level35% higher than would be desirable. Taking into account that thisincrease has a direct effect on the cost of the workpiece, this can beconsidered a serious problem, even more so if the part to be made has tobe made from materials with high value on the market such as copper orstainless steels. It has nevertheless been shown that the use of thistightening ring generates a loss in the planimetry of the finished part,since, when carrying out its “locking” function, this tightening ringalso prevents the release of the tensions caused by cutting the part.This means that reason these tensions cannot be passed on to the wasteor scrap, which would be more desirable. This problem is solved by thepresent invention.

In the stamping processes by the GRIP FLOW® system, the most seriousproblems are as follows:

The system is in itself designed for small and medium thicknesses, butis not suitable for manufacturing thicker parts in large production runsdue to its own configuration, as will be explained later.

The upper hydraulic cushion consists of at least two cylinders. Thiscushion is not steered by any guide element which guarantees itsperfectly vertical and synchronic movement. For this reason there is anunbalance problem which affects the position and movement of the upperstripper, either due to a fault in one of these or simply to internalfriction or pressure differences. This has a direct effect on theposition of stripper pins, both at the time of extension, for whichreason this directly affects the cushion bottoming die, the stripperpins and the upper stripper, and can damage this in its guide zone dueto the axial strains caused by the unbalancing as well as the punchesfor internal openings in the part, usually known as “piercing punches”.

The “axial locking” effect may result in the breakage of the cushionbottoming die, as well as the stripper pins, upper stripper, piercingpunch or the actual cutting die itself, affecting the tooling or thequality of the part.

The upper cushion bottoming die is thin and not guided. For this reasonthere are cases of this being jammed in both the compression and theextension cycle, directly affecting the tool and making this break, aswell as affecting the quality of the part.

The upper hydraulic cushion is inserted in a cavity and opposite this isits bottoming die, and in contact with this is the upper plate of thedie shoe commonly known as “Die-set”. The GRIP FLOW® design places thecavity of the upper cushion just above the point where all the cuttingpressure, or tonnage necessary for this, is exerted. This means that atthe time when the part is cut the upper plate of the die-set is notsupported on its uppermost face, that is, on the face where it is incontact with the bottoming die of the upper cushion. This entails thatat the time of maximum effort, that is, at the point of cutting, thebottoming die is in a withdrawn position through the action of the upperstripper pins. For this reason the upper plate of the die-set is locatedjust in the area of contact with the bottoming die in the “air”, withnothing to overlap the upper plate of the “die-set” or withstand thestress to which this is being subjected at the time of cutting this, andthus preventing its deformation. The result of this lack of support oroverlapping is the permanent deformation of this plate in the contactarea of the bottoming die. This leads to all the plates forming theupper tool assembly being damaged due to the permanent deformation ofthe upper plate of the die-set which supports these. This has a directinfluence on the quality of the part and life of the tooling, since theeffect following this permanent deformation is that the other plateslose their flatness and thus their verticality and alignment. This meansthat the upper tooling “bites” into the lower tooling, graduallydeteriorating the tooling with each new cycle that is run.

The die-cutter extends along the whole useful surface of the tooling.This is formed of a plate of the same size as the punch holder plate orthe bottoming die plate of the tooling. The die consists of a platewhich performs the cutting action and a plate that supports this andguides the part after cutting its perimeter.

This design involves the problem that if there is any breakage of thedie or if this is seriously damaged, the whole plate will have to bereplaced with a new one, with the consequent costs.

The lower ejection plate passes on the movement driven by the presscarriage and due to the action of the stripper pins not being “guided”by any item guaranteeing the accuracy of its movement or itsverticality, resulting in jams and bites in the punch.

The lower cushion is made up of at least two hydraulic cylinders. Thiscushion is not steered by any guiding item guaranteeing its perfectlyvertical and synchronic movement. For this reason there is anunbalancing problem affecting the position and movement of the lowerstripper pins and thus of the lower stripper in respect of the punch, sothat the stripper can bite the punch in its upward expulsion movement,damaging this punch.

The punch is located on a lower plate of the die shoe; this plate ismade of soft material, i.e. not hardened or hardened, and the punch willthus “stick into” this plate through the effect of the cutting pressure.

The punch is secured at the bottom of the tooling to prevent this frombeing pulled off at the time of ejection. In spite of the punch having aflange facilitating securing this, there is a problem of securing thispunch for parts that have little wall between the outside of the partand the inner cutaway, not having sufficient surface area to house anyscrews of sufficient size to support the traction stress of strippingthe scrap or the remains of the outside strip of the punch, for whichreason making this without the flange is not feasible, and itsmanufacturing is thus more expensive.

The lower part of the tool, according to U.S. Pat. No. 6,370,931,consists of a punch, a lower stripper, stripper pins and a lower dieshoe or “die-set”. This assembly rests on a plate which corresponds tothe press bed, and this bed has a through-bore of considerable size toallow the scrap or cuttings through. There is thus the deformationproblem mentioned above. In this case the plate rests on the die shoe,but there is no support in the cutaway area of the plate and the dieshoe thus deforms through the effect of the cutting pressure and thetonnage exerted just in this area stemming from the stress on the punch,this plate being permanently deformed in this area; this affects thesupport of the punch, which loses alignment and verticality, causing theconsequent “bite” on the die in the successive cycles due to theextremely limited tolerances between punch and die, and permanentlydamaging the tooling.

Precision stamping requires the balancing of both the upper and lowerparts of the die, since when there is any unbalance two unwanted effectsare produced: the first effect is the loss of accuracy in stamping theparts and the second effect is the greater wear of the dies, and thus anincrease in the production cost and reduction in productivity.

DESCRIPTION OF THE INVENTION

This invention refers to a stamping press which solves all the problemsmentioned above, enabling high accuracy and durability of the dies, andsafety in removing the scrap, ensuring greater stability in makingparts.

The press according to the invention comprises:

-   -   A fixed lower body, which comprises a machine bed;    -   A mobile upper body, known as the press carriage;    -   A body that is mobile in respect of the fixed lower body (lower        cushion);    -   A body that is mobile in respect of the mobile upper body (upper        cushion);    -   A die-cutting set made up of an upper part of the die-cutting        set integral with the mobile upper body and a lower part of the        die-cutting set fixed to the machine bed; and    -   A device for guiding the upper part of the die-cutting set in        respect of the lower part of the die-cutting set.

At the top the machine bed has a housing for a lower adapter plate. Atthe bottom it also has a support or housing for a lower bottoming dieapart from a set of through-bores for allowing stripper pins through.

The lower adapter plate also has a set of through-bores for allowing thestripper pins through, as well as holes for allowing the scrap orcuttings out. This lower adapter plate prevents the deformation of thelower die shoe plate. This adapter plate will normally be made of steel.

The lower bottoming die is located at the bottom of the machine bed andalso has through-bores for allowing through the stripper pins and forletting out the scrap or cuttings, the latter being a single large hole.Said lower bottoming die will be made of hardened steel. Said lowerbottoming die has the purpose of preventing any permanent deformationson the lower part of the machine bed through impacts on the lowercushion in each expulsion cycle of the stamped parts. If saiddeformations were to arise through continuing use it is possible toreplace said lower bottoming die, without needing to replace the bed.

The lower cushion is made up of a single central and hollow hydrauliccylinder, with an annular section. The central bore of said lowercushion enables the expulsion of scrap or cuttings down through thiswithout the decompensation or unbalance existing in devices with lowercushions made up of multiple cylinders. The hydraulic cylinder ispreferably dual action, meaning that the movements and accelerations canbe controlled, this being particularly advantageous for reducing theimpact on the lower bottoming die of the bed. The hydraulic cylinder isprovided with a position-detecting device, such as an encoder.

The lower part of the die-cutting set is made up of a lower die-cuttingset plate, a lower bottoming die of the die-cutter, a lower punch holderplate and possible a punch press plate, a punch and a lower stripper.The punch holder plate is used for positioning the punch. In some casesthe punch simultaneously performs the functions of the die. If the punchis not of the appropriate size to be held at the bottom with screwfittings, then an additional plate known as a punch press can be used.This comprises means for holding the punch by locking this, said holdingmeans being made up of one or more parts. This lower punch holder plateas well as the punch press plate will where applicable be located on alower bottoming die of the die-cutter. If the punch can be held only bymeans of screws the lower punch holder plate will be needed forpositioning this. The lower part of the die-cutting set comprises alower stripper. Said lower stripper is provided with stripper pins fordriving the expulsion movement, and guide columns which slide alongguide bushes, guaranteeing perfect balance and high accuracy in thevertical movement of the lower stripper.

The upper cushion comprises a base plate on which there is a single dualaction hydraulic cylinder which has a hardened bottoming die fitted atthe bottom to prevent the deformation of this hydraulic cylinder throughthe effect of the stress of the transmission pins of the carriageadapter plate. The hydraulic cylinder can be dual action, so that themovements and accelerations can be controlled. The hydraulic cylinder isalso provided with a device for position detection, such as an encoder.

The base plate comprises a housing for a plate for adaptation to thecarriage. This plate comprises through-bores for housing transmissionpins, which are known as transmission pins for the plate for adaptationto the carriage.

This plate for adaptation to the carriage can be secured by screws or bya fast-release device.

Both the base plate and the plate for adaptation to the carriage can befixed to an upper die-cutter holder plate.

Fitted to this upper die-cutter plate is an upper bottoming die for thedie-cutter, an upper punch holder plate, an upper guide plate and anupper die shoe plate. All these plates are made of hardened steel.

Secured to the upper die shoe plate there is an upper die. On theinterior, in the die and the upper guide plate there is an upperstripper which slides through these parts. On the upper punch holderplate one or more piercing punches are fitted, through which the upperstripper slides. This stripper extends by means of transmission pins ofthe upper stripper which cross the set of plates forming the upper partof the die set and which rest on the transmission pins of the plate foradaptation to the carriage.

The expulsion of the die-cut part is performed through the action of thehydraulic cylinder of the upper cushion, through the upper bottoming dieand the transmission pins of the plate for adaptation to the carriageand of the transmission pins of the upper stripper, which act directlyon the stripper.

Both the bottom and top part of the die-cutting assembly are fitted onpins to guarantee their respective alignment.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to illustrate the following explanation, we adjoin to thisdescriptive report four sheets of drawings in which the essence of thisinvention is represented in eight figures and in which:

FIG. 1 shows a schematic cross-section view of the stamping press of theinvention;

FIG. 2 shows a detail of a first device for securing the punch, as anexample;

FIG. 3 shows a detail of a second device for securing the punch, as anexample;

FIG. 4 shows a detail of the assembly of the punch, by means of screws.

FIG. 5 shows a view of a stamping press of the earlier GRIP FLOW® systemin which one can appreciate the unbalancing of the lower cushion causedby an oil leak, a differential wear of the hydraulic cylinders, adifferential in the internal friction, different load losses in thehydraulic lines or other causes;

FIG. 6 shows a detail of the theoretical position of the lower stripperover the lower punch in the machine of FIG. 5;

FIG. 7 shows a detail of the real effect caused when the lower stripperundergoes a slight unbalancing, according to the preceding state of theart of FIGS. 5 and 6; and

FIG. 8 shows a detail of a “bite” caused in the punch by the lowerstripper due to the unbalancing of the lower cushion, according to thesystem of FIGS. 5 to 7.

DETAILED DESCRIPTION OF A PREFERENTIAL FORM OF EMBODIMENT

According to a preferential form of embodiment of the invention, astamping press for a laminated metal material (28), such as a strip, isdescribed, comprising:

-   -   a fixed lower body provided with a machine bed (17);    -   a lower cushion which constitutes a mobile body in respect of        the fixed lower body;    -   a base plate of the lower cushion (37), which will be fixed to        the machine bed (17); the lower cushion comprises a single        hydraulic cylinder (34) with an annular section placed in the        central part of the machine bed; the hydraulic cylinder (34) is        hollow in the centre and this hollow area constitutes a zone for        removal of any scrap or cuttings produced by the die-cutting        performed in the stamping process; through being a single        central hydraulic cylinder, the problems stemming from unbalance        are ruled out; the lower cushion is driven by means of oil        pressure stemming from the pressure line (38) to move the        hydraulic cylinder upwards, or the pressure line (36) to move        this downward. The hydraulic cylinder (34) also comprises a        device for reading the lower position, such as an encoder (20);    -   a mobile upper body or press carriage (21); this mobile body is        driven by the main hydraulic cylinder of the press (41).    -   an upper cushion which constitutes a mobile body in respect of        the upper mobile body. This upper cushion is for ejecting the        part and/or deforming this prior to cutting when this is        required;    -   a die-cutter assembly consisting of the top part of the        die-cutting assembly fixed to the upper mobile body, and a lower        part of the die-cutting assembly integral with the machine bed;        and    -   A guiding device (27) for the top of the die-cutting assembly in        respect of the bottom part of the die-cutting assembly.

The bottom part of the die-cutting assembly is made up of:

-   -   A lower die-cutter holder plate (16) which houses guide columns        (27);    -   a lower bottoming die (14);    -   a lower punch holder plate (31);    -   a punch press plate (32);    -   a punch (15);    -   a lower stripper (29);    -   a set of lower transmission pins (30);    -   a set of guide bushes of the lower stripper (39); and    -   a set of guide columns of the lower stripper (40).

The top part of the die-cutting assembly is in turn made up of:

-   -   an upper die-cutter holder plate (6) which houses guide bushes        (7);    -   an upper bottoming die plate (8);    -   an upper punch holder plate (9);    -   an upper guide plate (10);    -   an upper die shoe plate (11);    -   an upper die (12);    -   an upper stripper (13);    -   transmission pins of the upper stripper (26).

The press according to the invention comprises a lower adapter plate(18), placed in a housing made in the machine bed (17), said loweradapter plate (18) being provided with through holes for removing thescrap or cuttings, as well as for the lower stripper transmission pins(30) to go through. Said lower adapter plate (18) is used to prevent thetemporary or permanent deformation of the lower die-cutter holder plate(16), as well as the set of plates that are fitted on this (lowerbottoming die (14), lower punch holder plate (31), punch press plate(32)), also preventing the misalignment or loss of verticality of thepunch (15).

The stamping press of the invention also comprises a machine bedbottoming die (19), set at the bottom part of the machine bed. Thismachine bed bottoming die (19) prevents the deformation of the bottompart of the machine bed through being pressed by the bottoming die ofthe lower cushion (33) in each cycle.

The lower cushion bottoming die (33) is fitted integral to the top partof the hydraulic cylinder (34) with an annular section.

The press carriage (21) comprises a base plate of the upper cushion (3)provided with an upper cushion. The upper cushion comprises:

-   -   a hydraulic cylinder for the upper cushion (23); a position        detection device, such as an encoder (1);    -   a plate for adaptation to the carriage (5) set in the base plate        of the upper cushion (3); this plate for adaptation to the        carriage (5) prevents the deformation of the upper plate of the        die-cutter holder (6), and thus also prevents the deformation of        the top part of the die-cutting assembly and the ensuing        misalignment;    -   transmission pins of the plate for adaptation to the carriage        (24) whose base is housed in the plate for adaptation to the        carriage (5); and    -   an upper cushion bottoming die (4); this bottoming die will        normally be made of hardened steel and be secured to the        hydraulic cylinder of the upper cushion (23); this bottoming die        is for preventing the deformation of the hydraulic cylinder of        the upper cushion (23).

The hydraulic cylinder of the upper cushion (23) has the function ofpushing the transmission pins of the plate for adaptation to thecarriage (24) and the transmission pins of the upper stripper (26). Saidupper cushion hydraulic cylinder (23) is driven by pressure lines (22,42), which respectively have a pushing and braking effect.

The upper die shoe plate (11) houses the die plate (12), which meansthat a more expensive and stronger material can be used for the die, andin the event of breakage only the spoiled part can be replaced; in thecase of multiple cavities (for multiple upper dies), only the affectedpart and not the entire dies can be replaced, significantly reducing theoperating and maintenance costs. Similarly, the lower punch holder plate(31) can comprise different cavities in which different punches (15) arehoused, in agreement with the upper dies or cavities.

The top part of the die-cutting assembly normally also incorporates oneor more piercing punches (25); it is nevertheless possible for saidpiercing punches (25) not to be present when their use is not necessaryfor making the required part.

It should be pointed out that both the upper cushion hydraulic cylinder(23) and the hollow hydraulic cylinder for the lower cushion (34),comprise internal guides for proper guidance of the movement of thecorresponding plungers as well as external scrapers for removing dirt.

The punch (15) can be secured directly to the lower die-cutter holderplate (16), for example by means of screws crossing the lower bottomingdie of the die-cutter (14). This solution can be seen in the diagram inFIG. 4. When the geometry or dimensions of the parts to be made meanthat this securing system is not feasible it is also possible to use thefixing device, such as a securing part (323) fitted with a variableshaped flange (322) or with a housing for a ring (321), the punch (15)comprising a recess for partly housing said ring (321), with thesecuring piece (323) being the one that is secured to the lowerdie-cutter holder plate (16) or to the lower bottoming die of thedie-cutter (14) by means of screws.

What is claimed is:
 1. A stamping press, which comprises: a fixed lowerbody provided with a machine bed; a mobile upper body; a lower cushionwhich constitutes a mobile body in respect of the fixed lower body; anupper cushion which constitutes a mobile body in respect of the mobileupper body; a die-cutting assembly having a top part thereof integral tothe upper mobile body, and a bottom part thereof integral to the machinebed; a guiding device for guiding the top part of the die-cuttingassembly in respect of the bottom part of the die-cutting assembly;wherein the lower cushion comprises a single hydraulic cylinder with anannular section placed in a central part of the machine bed, having ahollow central part constituting a zone for removal of scrap andcuttings produced by a die-cutting operation performed in the stampingpress.
 2. A stamping press, according to claim 1, further comprising alower adapter plate fitted in a housing made in the machine bed, saidlower adapter plate being provided with through-bores for removal of thescrap and cuttings, as well as for allowing transmission pinstherethrough of a lower stripper incorporated in said press.
 3. Astamping press, according to claim 1, further comprising a bottoming dieof the machine bed, fitted in a bottom part of the machine bed.
 4. Astamping press, according to claim 1, further comprising a bottoming dieof the lower cushion joined to the hydraulic cylinder.
 5. A stampingpress, according to claim 1, wherein: the mobile upper body includes: abase plate of the upper cushion; a bottoming die of the upper cushion;and a hydraulic cylinder for the upper cushion; a position detectiondevice; a plate for adaptation to the mobile upper body fitted on thebase plate of the upper cushion; and transmission pins of the base platefor adaptation to the mobile upper body.
 6. A stamping press, accordingto claim 1, wherein the bottom part of the die-cutting assembly is madeup of the following connected parts: a lower die-cutter holder platewhich houses guide columns; a lower bottoming die; a lower punch holderplate; a punch press plate; a punch; a lower stripper; a set of lowertransmission pins; a set of guide bushes of the lower stripper; and aset of guide columns of the lower stripper.
 7. A stamping press,according to claim 6, wherein the punch press plate comprises a flangefor holding the punch; and the punch has a recess for insertion of thisflange.
 8. A stamping press, according to claim 1, wherein the top partof the die-cutting assembly is made up of the following connected parts:an upper die-cutter holder plate which houses guide bushes; an upperbottoming die plate; an upper punch holder plate; an upper guide plate;an upper die shoe plate; an upper die; an upper stripper; andtransmission pins of the upper stripper.
 9. A stamping press, accordingto claim 8, wherein the top part of the die-cutter assembly alsocomprises at least one piercing punch.
 10. A stamping press, accordingto claim 5, wherein both the hydraulic cylinder of the upper cushion andthe hollow hydraulic cylinder of the lower cushion, comprise internalguides for guiding movement of corresponding plungers and externalscrapers for removing dirt.
 11. A stamping press, according to claim 6,wherein the lower punch holder plate comprises a plurality of cavitiesin which different punches are housed.
 12. A stamping press, accordingto claim 8, wherein the upper die shoe plate comprises a plurality ofcavities in which different upper dies are housed in accordance withdifferent lower punches housed in cavities of a lower punch holderplate.
 13. A stamping press, according to claim 6, wherein the punch isanchored to the lower die-cutter holder plate by a securing partprovided with a flange, the securing part being fixed to one of: thelower die-cutter holder plate and the lower bottoming die of thedie-cutter.
 14. A stamping press, according to claim 6, wherein thepunch is anchored to the lower die-cutter holder plate by a securingpart with a housing for a ring, the punch comprising a recess forpartially housing said ring, the securing part being fixed to one of:the lower die-cutter holder plate and the lower bottoming die of thedie-cutter.